The desirability of a device capable of detecting the center of rotation of a rotating object is frequently felt and urged in numerous industries and various branches of the science of measurement. Particularly in the operation of precision machining by the use of a lathe, for example, the detection of the center of rotation of the worked surface of a rotating workpiece constitutes one of the essential tasks indispensable to the machining operation. The critically precise finishing generally accomplished by rotating the workpiece about its axis and advancing a cutting tool such as a diamond tool secured on the cutter holder of a lathe from the periphery of the workpiece toward the center of rotation thereof. If, in this case, the center of rotation of the workpiece is not accurately known, there may occur a portion around the axis of the workpiece which escapes being cut by the tool. To avoid this situation, the lathe operator makes a point of aligning the tip of the tool to the dead center before starting the operation of the lathe and, thereafter, advancing the tool from the periphery of the workpiece toward the center of rotation all over again. This job requires advanced skill and consumes much time.
One conceivable practical method for effecting automatic detection of the center of rotation of a rotating object may comprise sequentially detecting the center of rotation of the workpiece during the process of machining and feeding the results of detection back to the control system which serves to drive the tool or other cutting edge. Actually, however, there has not yet been developed a device which is capable of effecting such an automatic detection of the center of rotation of a rotating object as described above.
This invention has originated in the conception of an idea of utilizing the laser Doppler effect capable of measuring with high accuracy the velocity of rotation of a moving object to the detection of the center of rotation of a rotating object. To be more specific, since the center of rotation of a rotating object produces no movement, the detection of this center of rotation ought to be accomplished by illuminating the rotating object with laser beams and, from among the reflected laser beams, singling out the laser beam which has been free from the Doppler shift. The point at which the surface of the rotating object has reflected this particular laser beam undergoing no Doppler shift is the center of rotation in question. To meet the demand for more speedy detection of the center of rotation and for further simplification of measurement, however, the present approach has many problems yet to be solved. Worse still, since the laser beam which is reflected at the center of rotation of the rotating object is not subject to the Doppler shift, the reflected signal which has undergone a minute shift or absolutely no shift completely overlaps the pedestal component which inevitably appears as a noise component on the power spectrum, making it impossible to measure the amount of shift. Because of these difficulties, no success has yet been achieved in the application of the principle of the laser Doppler effect to the detection of the center of rotation of a rotating object.